Mercury
Mercury is the closest planet to the Sun, and for this reason it
has a very short year. Its days are quite long, though, because the
planet revolves around its own axis very slowly. Due to both these factors,
Mercury has just one day for each two years. It was named after the
Greek god of commerce and travel, most likely because of its orbital
velocity. The planet has a high temperature range, varying between -180°C
to 530°C, and is the highest temperature range for any body in the
Solar System. Despite this, radar observations of Mercury have shown
signs that water and ice may be evident on some craters at the North
Pole, which are shaded from the Sun.
The atmosphere of Mercury is very thin, and is largely made up of atoms
blasted off by solar wind. These atoms escape the atmosphere very fast
due to Mercury's hot surface, and create a significant drop in temperature.
The planet is predominantly made up of a large iron core, approximately
3700km in diameter, which contributes to Mercury's high density and
is also the reason why Mercury is some times referred to as the "Iron
planet". Mercury is similar to the Moon in that it has a number
of rather old craters, and it has no plate tectonics. Mercury's surface
is very irregular, as it has numerous cliffs and pits lining it. These
were created when Mercury's core cooled and shrank and the effect of
this was buckling of the planet's crust. Mercury has no known satellites.
Diameter
|
4,880 km
|
Mass
|
3.3 × 1023 kg
|
Mean Distance from sun
|
57,910,000 km
|
Mean Density
|
5.43 g/cm3
|
Rotational Period
|
59 Earth days
|
Orbital Period
|
88 Earth days
|
Mean Orbital Velocity
|
48 km/s
|
Atmosphere
|
50% oxygen, 30% sodium,
10% helium, 10% others
|
Average Surface Temperature
|
179°C
|
Equatorial Surface Gravity
|
3.7 m/s2
|
|